Presently, the use of hydrocarbon fuels, such as JP-4, JP-5, diesel and gasoline, in military fixed and rotary wing aircraft, as well as in ship and ground vehicles, is a necessity in the defense of our country. In combat situations, vehicle fuel tanks containing these fuels are frequently exposed to enemy fire, which can cause penetration of the fuel tanks by fragment, ball, Armor Piercing (AP) projectiles, Armor Piercing Incendiary (API) and High Explosive Incendiary (HEI) projectiles. The projectile calibre range from small arms (7.62 and 12.5 mm, as well as 0.30 and 0.50 CAL projectiles) to anti-armor and anti-personnel (12.5, 14.7, and 20 mm projectiles) to anti-aircraft shells, mortar, grenades, and missiles (surface-to-air and air-to-air). The penetration and entry of these projectiles and/or the detonation of the High Explosive (HE) and HEI projectiles and/or their fragments into vehicular, and stationary, hydrocarbon fuel storage tanks can cause the hydrocarbon fuels to ignite and burn.
At present, the most effective gaseous fire extinguishing system available is the HALON class of fire extinguishers. Since the discovery in 1839 of HALON 104 (carbon tetrachloride, CCl.sub.4), its usage to fight electrical fires, as well as the other halogen containing family of flame retardants and extinguishing agents, have found wide usage and acceptance within the civilian and military communities, e.g. HALON 1301, (CF.sub.3 Br) and HALON 1211 (CF.sub.2 BrCl). The role of the halogen elements (fluorine, chlorine, bromine and iodine), to extinguish the flame has been studied and well documented. The most effective and widely used fire extinguishing agents contain bromine such as the 1301 and 1211 HALONs. These materials thermally decompose in a fire or flame to produce the bromide anion (Br.sup.-) which disrupts the chain reactions in the burning process.
It is known that the combustion process of hydrocarbon fuels contained within storage tanks occurs in the vapor state above the liquid hydrocarbon fuel. The flame radiates heat back to the liquid fuel and causes the liquid fuel to become vapor. Between the liquid fuel and the flame, the intense heat causes the vaporized hydrocarbons to fragment producing molecular fragments or hydrocarbon radicals, such as CH.sub.3., CH.sub.2., H.sup.+, etc., which can combine with the atmospheric oxygen in the flame, producing additional heat energy.
The role of the bromide anion (Br.sup.-), produced by the thermal decomposition of a HALON, is to disrupt the chain reactions. Possible reaction mechanisms include the hydrogen cation (H.sup.+) combining with the bromide anion (Br.sup.-) to form HBr which then can react with the OH.sup.- anion to produce water (H.sub.2 0), and the bromide anion (Br.sup.-) thereby interrupting the combustion process chain reaction and regenerating the bromide anion (Br.sup.-). Bromine containing compounds, particularly the gaseous or low boiling point HALONs, are very effective fire extinguishing agents.
However, due to environmental reasons, (depletion of the upper atmosphere ozone layer) the usage of the HALON class of fire extinguishing agents is presently decreasing, and must continue to decrease. The ban on the manufacture of HALONS begins on Dec. 31, 1994 and the ban on chlorofluorocarbons (CFCs) begins Dec. 31, 1995. There is, therefore, a degree of urgency that an alternate fire extinguishing system be developed that is not dependent upon the HALONS.
When burning of hydrocarbon fuel, the combustion process, can be interrupted or stopped by one or more of the following actions: (1) Remove heat at a greater rate than it is being generated; (2) Prevent fuel from feeding the fire; (3) Lowering the oxygen concentration within the fire by diluting entering air with inert gases, the most outstanding of which is carbon dioxide; and, (4) Interrupt flaming-combustion chain reactions without fuel removal, direct cooling or oxygen dilution.
Since the area under consideration contains the fuel, the prevention of fuel from feeding the fire (Action 2) is not possible. The present invention employs primarily the first and third of these actions by introducing nitrogen, water vapor, and oxides of carbon gases when fire, flame, fireball, heat, and/or an increase in pressure are detected. To further enhance the fire fighting capabilities of the system, the fourth approach, usage of off-the-shelf fire inhibitors, can be used as an adjunct to the on-demand generation of gases and vapors reactions.
The most logical of these actions that could be performed on a military vehicle environment would be to remove heat at a greater rate than it is being generated and to lower the oxygen concentration within the fire area by diluting entering air with inert gases.
The present invention differs from other approaches to achieve these goals by using fast chemical reactions to produce the gases and water vapor when required, e.g., the burning of a propellant or the deflagration (low order detonation) of an explosive. In the present invention, the chemical composition of the propellant for explosive is selected to optimize both, the burning or deflagration rate and their chemical decomposition products. The on-demand nitrogen and water vapor chemical reaction generators of the present invention will simplify existing hardware, eliminate the need for high pressure gas cylinders, and the usage of high detonating rate, primary explosives inside the combat vehicle or aircraft fuel tanks.
The Cartridge Actuated Device (CAD) technology and hardware now available will permit the location of the gas generator for the present invention either, inside the hydrocarbon fuel tank or outside, with the distribution tubing and detection system located inside the fuel tank. CADs, with very slow burning rate chemical formulations, can be used to blanket the liquid hydrocarbon fuel and to increase the percentage of nitrogen gas in the vapor phase before entering the combat zone. A slow rate of production but continuous supply of nitrogen gas is required to replace the volume of the hydrocarbon fuel burned by the aircraft engines.
Non-energetic flame retardant chemicals also can be added to the propellant or explosive formulations, or they can be dispersed into the fuel tank by the expanding gaseous combustion products of the explosive or propellant.
Accordingly, it is an object of the present invention to provide a non-HALON fire extinguishing system causing a decrease in the atmospheric oxygen content, so that burning of hydrocarbon fuels cannot be sustained.
Another object of the present invention is a fire extinguishing system chemically balanced to optimize the production of nitrogen, carbon monoxide and carbon dioxide gases and water vapor.
A further object of the present invention is a gas generating fire extinguishing system for reducing the available atmospheric oxygen in the vicinity of a potential hydrocarbon fuel fire, to such an extent that combustion of the fuel will not be sustained.
An additional object of the present invention is an on-demand, non-HALON, fire extinguishing system.
A still further object of the present invention is an on-demand gas generation system that employs inert gases, water vapor and solid fire inhibitor additives in a fire extinguishing system.
An additional object of the present invention is a fire extinguishing system for hydrocarbon fuel fires that employs an explosive and/or a propellant to engulf the fuel supply in a reduced oxygen atmosphere that will not sustain combustion.
Another object of the present invention is a gas generating system that fills all space in a hydrocarbon fuel tank that is not filled with fuel with a mixture of inert gases, water vapor and flame inhibiting chemical additives.